In most RF applications, discrete P-i-N diodes are used in RF switch arrays because they have the correct diode characteristics to operate correctly. However, using discrete P-i-N diodes increases both the size and the cost of the RF switch arrays. Another impact of using discrete P-i-N diodes is that a discrete RC circuit is needed to isolate the P-i-N diode from a driver chip that will be used to drive the P-i-N diode. Therefore, it would be preferable to use integrated diodes in building RF switch arrays but current technological limitations have prevented their use. This is because current CMOS integrated diodes are not capable of sustaining the performance requirements necessary for the RF switch array.
To solve some of the above stated problems a technique has been found which allows for the fabrication of a CMOS integrated diode, such as that disclosed in U.S. Pat. No. 5,757,065 and assigned to the assignee of the present application. U.S. Pat. No. 5,757,065 entitled HIGH VOLTAGE INTEGRATED CIRCUIT DIODE WITH A CHARGE INJECTING NODE discloses using an injecting node in a CMOS integrated diode for producing diode characteristics more closely resembling the characteristics of a discrete P-i-N diode. Additionally, these integrated P-i-N diodes need electronic driver circuitry for biasing the injecting node for proper switching. The P-i-N diode characteristics, which in turn directly determine the efficiency of RF switching in Acoustic Ink Jet Printing (AIP) systems, are extremely sensitive to temperature and process parameters variations. Therefore what is needed is a design for the driver circuitry such that those inefficiencies due to process parameters and temperatures variations are compensated and canceled out.
In accordance with the present invention, there is provided an electronic driver circuitry for an RF switch diode used in Acoustic Ink Jet Printing (AIP) systems that compensates and cancels out undesired variations and non-idealities. The electronic driver circuitry consists of a PMOS transistor and a poly resistor used to control the on/off states of the RF switch diode wherein the drive current for the RF switch diode is the same as the current in the PMOS transistor. To compensate for undesirable variations in the RF switch diode, the driver circuitry is designed such that the current in the PMOS transistor is adjusted in an opposite direction to cancel the unwanted variations.